U.S. Pat. No. 6,232,672 discloses a handheld work apparatus whose drive motor drives a generator. The generator supplies power for the operation of a heating unit. The generated generator power varies depending on the rotational speed. At low rotational speeds only a small amount of power is available; at high rotational speeds, however, a large amount is available. The heating element is configured in this case such that, at low rotational speeds, sufficient heating can be achieved, in order, for example, in the case of a carburetor heater, to avoid air humidity from the surroundings freezing on the housing of the carburetor. At high rotational speeds, it must be ensured that no overheating of the carburetor takes place because, with a carburetor heater, overheating can lead to the formation of vapor bubbles in the fuel and thus to an unstable operating behavior of the combustion engine.
In order to control the temperature in known heating elements, temperature switches are used such as bimetallic switches, for example. In order to measure the heat in the component to be heated, the temperature switch must, however, be at a certain distance from the heating element itself. As a result, the temperature switch reacts sluggishly. When the heating element is operated with very high power, for example, at full-load of the drive motor, it is not possible to achieve satisfactory temperature control on account of the sluggishness of the temperature measurement. Therefore, in the case of a carburetor heater, disruptions can occur before the temperature switch responds during operation of the heating element with very high power. Furthermore, known temperature switches have a hysteresis which leads to large temperature fluctuations at the heating element itself.